From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Mon, 25 Aug 2008 18:54:37 -0700 (PDT) Received: from cuda.sgi.com (cuda2.sgi.com [192.48.168.29]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id m7Q1sUEX012342 for ; Mon, 25 Aug 2008 18:54:31 -0700 Received: from ipmail01.adl6.internode.on.net (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id 0DC713CD48C for ; Mon, 25 Aug 2008 18:55:53 -0700 (PDT) Received: from ipmail01.adl6.internode.on.net (ipmail01.adl6.internode.on.net [203.16.214.146]) by cuda.sgi.com with ESMTP id Dv77OX9UipMuZOGW for ; Mon, 25 Aug 2008 18:55:53 -0700 (PDT) Date: Tue, 26 Aug 2008 11:55:49 +1000 From: Dave Chinner Subject: Re: [2.6.27-rc4] XFS i_lock vs i_iolock... Message-ID: <20080826015549.GT5706@disturbed> References: <6278d2220808221412x28f4ac5dl508884c8030b364a@mail.gmail.com> <20080825010213.GO5706@disturbed> <48B21507.9050708@sgi.com> <20080825035542.GR5706@disturbed> <1219647573.20732.28.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1219647573.20732.28.camel@twins> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Peter Zijlstra Cc: Lachlan McIlroy , Daniel J Blueman , Linux Kernel , xfs@oss.sgi.com, hch@lst.de On Mon, Aug 25, 2008 at 08:59:33AM +0200, Peter Zijlstra wrote: > On Mon, 2008-08-25 at 13:55 +1000, Dave Chinner wrote: > > On Mon, Aug 25, 2008 at 12:12:23PM +1000, Lachlan McIlroy wrote: > > > Dave Chinner wrote: > > >> On Fri, Aug 22, 2008 at 10:12:59PM +0100, Daniel J Blueman wrote: > > >>> ======================================================= > > >>> [ INFO: possible circular locking dependency detected ] > > >>> 2.6.27-rc4-224c #1 > > >>> ------------------------------------------------------- > > >>> xfs_fsr/5763 is trying to acquire lock: > > >>> (&(&ip->i_lock)->mr_lock/2){--..}, at: [] xfs_ilock+0x8c/0xb0 > > >>> > > >>> but task is already holding lock: > > >>> (&(&ip->i_iolock)->mr_lock/3){--..}, at: [] > > >>> xfs_ilock+0xa5/0xb0 > > >> > > >> False positive. We do: > > >> > > >> xfs_lock_two_inodes(ip, tip, XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL); > > > > > > Why not just change the above line to two lines: > > > xfs_lock_two_inodes(ip, tip, XFS_IOLOCK_EXCL); > > > xfs_lock_two_inodes(ip, tip, XFS_ILOCK_EXCL); > > > > Yeah, that'd work, but it implllies that we no longer allow > > xfs_lock_two_inodes() to take both inode locks at once. > > How can you take two locks in one go? It seems to me you always need to > take them one after another, and as soon as you do that, you have > ordering constraints. It doesn't take them both inode locks in one go - it does them separately in a given order via xfs_ilock(). Basically there are two layers of constraints here - xfs_ilock() handles the order withing a given inode, xfs_lock_two_inodes() handles order and deadlock prevention between inodes. What lockdep is complaining about is a difference in the lock order between different locks in different inodes - a situation that does not result in a deadlock... Cheers, Dave. -- Dave Chinner david@fromorbit.com